David Motton

Doing the maths to find out what tow car is right for you isn't always as easy as it sounds, so Practical Caravan's expert David Motton is here to help

Better to be cautious than to underestimate the matching ratio

Deciding what tow car is the best for you and your caravan takes some time and effort. It helps to have the right facts and figures to hand. Sometimes, though, these numbers aren't what they seem.

Take kerbweights. Finding out the kerbweight of any potential tow car is vital in deciding whether it will make a suitable tug for your caravan, since both major caravanning clubs recommend towing no more than 85% of your car's kerbweight. That's especially true for new and inexperienced tow car drivers.

Once upon a long time ago the kerbweight was defined as the weight of a vehicle in ready to use condition with a full tank of fuel. This was quite straightforward, easy to understand and simple to replicate if taking your own car to a weighbridge.

Now car manufacturers use the European Directive 95/48/EC. This defines the kerbweight (although it's referred to as the Mass in Running Order in the directive) as the car in ready to drive condition with a 90% full fuel tank, and an allowance of 68kg for the driver and 7kg for a small amount of luggage. For simplicity's sake, these allowances are often bundled together and referred to as 75kg for the driver.

What really makes it difficult to compare one car's kerbweight with another's is that not all manufacturers include the 75kg in their published weights. Some make it in the payload instead.

As if that wasn't enough, certain manufacturers (I'm looking at you, Vauxhall) have a habit of not publishing the kerbweight in their brochures at all, making safe and sensible matching of car and caravan unnecessarily difficult.

Some car makers, including Kia and Nissan, quote a range of kerbweights for the same model, depending on spec. I'm not talking about different weights for the same car with various engines and gearboxes, but a range of weights depending on whether or not you go for that full-length sunroof or the all-singing, all-dancing in-car entertainment system. So which weight should you use when deciding whether a car makes a suitable match for your caravan?

I'd be inclined to use the lower of the two, even though the chances are your car will weigh more. Better to be cautious than to underestimate the matching ratio and buy an unsuitable car.

The legal towing limit is another vital piece of data when shopping for a new tow car. However, there's more than one. Expect to find brochures and websites quoting a maximum figure for a braked trailer (like a caravan) and an unbraked trailer (such as a small box trailer).

Even when you have found the limits for a braked trailer there are often two, one for starting off on an 8% gradient and one for a 12% gradient.

If you see a car with blue flashing lights behind you and the driver wants you to stop for a chat, the nice friendly policeman won't want to see a copy of the brochure. If they think you are towing more than you should they'll check the weight plate on the car.

They'll find four figures. The third and fourth are the maximum axle loads. The first two show the gross vehicle weight (the most the car is permitted to weigh when loaded), the second shows the gross train weight (the most the car and its trailer/caravan are permitted to weigh in total).

Usually, if you take the gross vehicle weight from the gross train weight you'll have a number which matches the towing limit you so diligently checked when choosing your tow car.

However, this isn't always the case. Sometimes manufacturers sneakily quote the legal towing limit when the car is more or less empty. As soon as you start loading up, the effective towing limit drops.

The Citroën Grand C4 Picasso HDi 150 is a good example. The brochure says the legal towing limit is 1700kg. Load the car to its gross vehicle weight, and the towing limit effectively drops to 1400kg.

That doesn't make it a bad tow car. In fact, it's a very good one. But at best, this way of presenting the legal towing limit is confusing. At worst it is downright misleading.

It all means you really need to do your homework when buying a tow car. Finding the kerbweight isn't enough. Even the kerbweight, noseweight and legal towing limit aren't sufficient. You need to check the gross vehicle and gross train weights before you order your next tow car.